There is at least one instance where NBSP had best be treated
as a fixed width space, when it is used as thousands separator as in
100 000. Unicode recognizes it for this use by assigning NBSP the
Bidi Class of CS. I doubt if anyone is going to seriously argue that the
space between 100 and 000 should be expanded upon justification.
Of course, that could be taken care of by adding NBSP to Boundary
class MidNum in the Text Boundaries document (UAX#29) without
affecting its nature when used elsewhere.
